1. Field of the Invention
The present invention relates to an electric discharge machine in which a wire electrode is used as an electrode and which is suitable for electric discharge machining to vary a work area of a workpiece during the work.
2. Description of the Prior Art
The wire cut electric discharge machine controls an electric condition in the best condition depending upon variation of a thickness of a workpiece.
In the wire cut electric discharge machine, a metallic wire having a diameter of about 0.05 to 0.3 mm is used as an electrode to cause the relative movement in X-axis and Y-axis directions to the workpiece whereby the processing of cutting and boring in a desired configuration is carried out.
The relative movement is usually a stepped constant feed having the order of 1 .mu.m per pulse in the electric discharge whereby the electric discharge having a constant voltage is performed in a working gap without controlling an electric discharge energy. When a thickness of the workpiece is constant, the work can be carried out as desired, even though it is the constant feed. However, when a thickness of the workpiece is not constant, the work is firstly carried out with the feed speed set for the maximum thickness (maximum processing area) in order to prevent the trouble of shortcircuiting or wire cutting and accordingly, even though a thickness of the workpiece is reduced during the work, the electrode is fed at the initially set slow speed and the work efficiency is low.
Even though a thickness of the workpiece is constant, when the workpiece is processed in a configuration having a corner part, the corner is rounded and a sharp corner can not be disadvantageously given.
It has been proposed to control the work feed speed by detecting a voltage in the work gap, i.e. the work voltage in order to overcome the constant feed speed work. This is superior to the constant feed speed work, however, this does not attain satisfactory effect.